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ATTORNEYS United States Patent O U.S. Cl. 84-1.02 12 Claims ABSTRACT FTHE DISCLOSURE An audio frequency system for processing musical signals,particularly for reduction of intermodulation distortion produced bysimultaneous tones subsisting in relatively small sub-bands of the audiofrequency band, Iby subdividing the audio band in terms of quarteroctave filters, combining the outputs of those filters which haveprimarily octavely related partials into separate channels, andtransducing the signal content of the channels.

This application is a division of my application Ser. No. 351,427, filedMar. 12, 1964, and entitled Multiple Speaker Sound Output System forReducing Intermodulation Distortion. t

The present invention relates generally to systems for processingmusical sounds, in its electronic production, recording and/ orreproduction, and more particularly to systems for reduction ofintermodulation distortion produced by simultaneous tones subsisting inrelatively small sub-bands of the audio frequency band, while enhancingthe musical quality of the simultaneous tones.

A most important limitation of present high-fidelity music amplificationsystems is the necessity to reproduce simultaneously from the sameamplifier and loudspeaker tones lying in the same general region of theaudio-frequency spectrum. In systems of high quality it has beencustomary to divide the entire audio frequency range into two, three, oreven four broad bands, so as to avoid intermodulation distortion of thetype produced by simultaneous tones of widely different frequency.However the other principal form of undesirable intermodulationdistortion, (that produced by simultaneous tones within a few octaves ofeach other, has continued to degrade sound reproduction. These effectsare particularly noticeable in the radius and high-frequency ranges ofsound, because difference frequencies in intermodulation distortion aremuch more audible than the summation components. The sense of hearing israther insensitive to Weak sounds of very low frequency. Hence the toneswhich (in combination) generate disturbing distortion must be highenough in frequency for their difference to be in the order of 100cycles or more.

Another problem in sound reproduction systems, especially in largeauditoriums, has been to retain the desirable directionalcharacteristics designed into a loudspeaker of limited power-deliveringcapacity, when the power requirements substantially exceed the unitsscapacity. The obvious practice is to use a large number of similar unitselectrically in parallel, and to neglect the spectral degrada- Mice tionresulting from interference effects between waves from different units,and the highly directional beaming effect produced by a parallel arrayof similar units.

When music is to be produced (rather than reproduced)electro-acoustically, similar problems exist. One of the inherenteconomic advantages of electronic organs over pipe organs, for example,is that the tones can all be radiated acoustically from the same soundsource. However, there are disadvantages from a tonal standpoint whichare inherent in the single sound-source method of tone radiation, suchas (l) intermodulation distortion, (2) a deficiency in apparent size ofthe musical sound source (in comparison to the historical instrument),and (3) a lack of change in sound localization when different notes inthe scale are played. It is possible, of course, to have different notesof the same pitch come from audibly different location, eg. whendifferent loudspeakers are used for different divisions of the organ,but this does not provide for any motion of the sound source when thenote changes within the division;

One electronic organ system method which is used to increase theapparent physical size of the sources of sound is to use multiplesources in parallel. As in sound reproduction systems, this tends tobeam the sound toward the listeners more than a single source would.This is highly undesirable for organ music. Another expedient is toorient the sound sources toward reflecting surfaces, so as to increasethe ratio of reflected-to-direct sound. Installing the sources in amoderately reverberant tone chamber coupled to the auditorium is stillanother approach. These methods reduce acoustical efficiency, and reducethe tonal definition required for full appreciation of musicalsubtlettes such as transient effects in the tone.

Accordingly it is a principal object of my invention to produce orreproduce musical sounds with a minimum of intermodulation distortion.

A further object is to provide a broad smooth directional characteristicthroughout the musical frequency range, so that the tonal spectra at allnormal listening positions will closely resemble each other, and willalso be similar to the spectrum of the total power radiated from theloudspeakers. This will tend to make the direct sound and the generallyreflected sound similar in timbre.

A further object is to, provide motion for the musical source as thefrequency changes, and to provide spread for the musical source whenvarious non-octavely related frequencies are present.

A further object is to provide a system for musical spatial modulationeffects which are a rapidly changing function of frequency, i.e. whichvary greatly within the span of an octave.

The key to the solution of the above problems and to the attainment ofthe above objects is to be found in the nature and composition ofmusical sound, and in an acoustically novel subdivision of the audiblefrequency lrange. Simultaneous octavely related tones occur ratherfrequently in music. Their intermodulation products are not very seriousmusically because the distortion products of oc'taves are also octavelyrelated to the original tones. Consequently they are very difiicult todistinguish from the original combination of tones. An ideal radiationsystem for musical tone, from an intermodulation distortion standpointwould be one in which only octavely related tones are radiated together.Only in very large sound systems would this be economically feasible.Another musical factor, which is pertinent to my invention, is that thefrequency of occurrence of closely adjacent musical tones in combinationis very small. When such adjacent tones (e.g. E and F in the musicalscale) are played, the dissonance effects experienced by 'the listenerovershadow intermodulation distortion effects which, by comparison, areminor. Furthermore the more nearly adjacent are the tones played incombination, the lower the difference frequency becomes and (because theear is quite insensitive to low frequencies) the less audible andobjectionable the difference tones will be.

The above described combination of factors makes it advantageous tocombine the ideal twelve octavely related groups of musical tones intosix, four, or even three groups, and thus effect a reasonable compromisebetween the requirements for low intermodulation distortion and lowcost. Combination into three groups is not too advantageous, becauseminor thirds are rather common intervals, and are quite consonant incomparison to major second intervals, which are the largest combinedintervals (short of an octave) which will occur when there are fourmajor groups of octavely related tones. Electronic and electrocousticalsystems designed along these principles of frequency-range division andrecombination may be described by the terms octaphonic There arenumerous other principles and refinements in the present invention,which will become apparent as the details are disclosed.

Other objects, advantages and features of the invention will also becomemore fully apparent from the following description of preferredembodimentsjthereof, taken in conjunction with the appended drawings, inwhich:

FIGURE 1 is a block diagram of an octaphonic system of recording,according to the invention;

FIGURE 2 is a block diagram of a playback system useful with the systemof FIGURE 1;

FIGURE 3 is a block diagram of a system for reproducing octaphonicallymusic derived from a conventional one track record;

FIGURE 4 is a block diagram of a modification of the system of FIGURE 3,wherein simplifications have been effected;

FIGURE 5 is a block diagram of a modification of the system of FIGURE 3employing relatively few multiply resonant filters in place of manysingly reasonant lters;

FIGURE 6 is a block diagram of a system employing the octaphonicprinciple in a musical instrument which generates tone forms directly;

FIGURE 7 is a block diagram of a simplified modification of the systemof FIGURE 6;

FIGURE 8 is a block diagram of a formant type of electronic musicalinstrument employing the octaphonic principle;

FIGURE 9 is a schematic block diagram of a resonator type of electronicmusical instrument employing the octaphonic principle;

FIGURE 1'0 is a block diagram of a simplification of the system ofFIGURE 9;

FIGURE l1 is a block diagram of a harmonic synthesis type of electronicmusical instrument employing the octaphonic principle;

FIGURE 12 is a block diagram of a space modulation system for octaphonicsound production or reproduction equipment;

FIGURE 13 is a block diagram showing the locations of complex tonalcentroids relative to locations of the loudspeakers in an octaphonicsystem; and

FIGURE 14 illustrates an exemplary physical arrangement of theloudspeakers in an installation of a multimanual electronic organ of anoctaphonic type.

In sound recording and playback systems it is generally possible toprovide microphones and pre-amplifiers with remarkably good linearity ofresponse, so that one need not be particularly concerned withintermodulation distortion in the low-level part of the recordingsystem. However, the recorder amplifiers, the heads, and the mediumitself may introduce audible distortion products, and frequently do.Consequently it is highly desirable, if possible, to apply theoctaphonic method of frequency-range division ahead of the recorderamplifiers, as shown in FIGURE l.

In the system of' FIGURE 1, sound is picked up by microphone 1. Themicrophone output signal is amplified by pre-amplifier 2, from which theamplified output is supplied through common input 3 to a set ofquarteroctave filters 4-27, inclusive. These filters cover thefundamental frequency range from 32 to 2000 c.p.s. approximately.Another two or three octaves of filters would be needed to fill out theupper portion of the entire audiofrequency spectrum. The transmissioncharacteristics of these filters need not be perfect, from afrequency-range division standpoint. For example, a 10 db discriminationagainst frequencies in the adajcent passband is quite satisfactory forthe purpose of this invention, although 20 db would be desirable. Theoutputs of filters 4-27 are cornbined through isolating networks (notshown) into four octavely related groups, II, III, IV, V, which areseparately amplified by recorder amplifiers 28-31. The outputs lof therecorder amplifiers, together with appropriate signals for biasing therecording medium, are supplied individually to a four-channel head 32.,recording on tape 33, and

' comprising individual recording elements 32a, b, c, and d.

In greater detail, the filters 4-27 inclusive are each arranged to passa frequency span of three semitones of the musical scale. So, filter 4passes the fundamental of tones A6. At, B6, and nearby partials in the6th octave of tones in lower octaves, while adjacent filter 5 passesonly F46, G6, Gl, filter 6 passes D46, E6, F6 and 7 passes C6, Cll andD6. The four filters 4-7 encompass the entire 6th octave. The fourfilters 4-7 lead, respectively, to recorder elements 32a, b, c, d.

In essence, all the octaves follow the rule for the sixth octave, sothat, for example recorder element 32a records only partialscorresponding to A, Ait, B, in all of the octaves.

In playback, FIGURE 2, the tape 33 moves past fourchannel playback head34, and the four playback signals (octaphonic channels II-V) areamplified separately by playback amplifiers .3S-38 and radiated fromseparate loudspeakers 39-42. This system provides maximum economy forthe purchaser of playback equipment, because the frequency-rangedivision occurs in the recording part of the system. Only the recordingstudios require the filter set, and the users of the tapes and theplayback systems gain the advantages.

The quality of music recordings varies greatly in accordance with thecare employed and the equipment used in making the recording. However, arecorded track which is relatively free of intermodulation distortioncan be badly degraded by the reproducing system. This is particularlytrue when the reproduction is at high sound level, or when a very largeauditorium or arena must be filled by the sound reproduction. FIGURE 3illustrates how octaphonic frequency-range division can beadvantageously accomplished in reproducing from a singlechannelrecording of music. The system can, of course, be duplicated forstereophonic reproduction. Single-channel playback head 43 responds tothe single track recorded on tape 44, and preamplifier 45 provides thefull-range of the musical spectrum through common input 46 to the inputsof the filters 47-74. In this case the quarter-octave filters 47474separate the reproduced signal into quarteroctave bands which areoctavely combined (through isolation means not shown) in mixing circuitsII-V. Again, as in FIGURE l, the four octaphonic channels are amplifiedand radiated by amplifiers 75-78 and loudspeakers 79-82. Although it isless economical f-or the filter set to be in the reproducing system,there is one great advantage. Such a reproducing system can acceptprogram material from any recorded track. There is no problem ofcompatibility with the original recording system. However the octaphonicreproducing system cannot correct for TABLE 3 non-linear diStOrtOnSintherecording. Quarter-Octave Identification of the Partials of a ComplexTwenty-Harmonic Tone G1 Group II C, C#, D III D#, E, E

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48o 5 v :B4- 3o 961 o V M5135 6 TABLE 2 13 Quarter-Octave Grouping ofthe 14 Partials of Any Tone 15 II IV III V 16 It should be pointed outclearly that the octaphonic 7 lter system does not direct all of thepartials of a com- 8 plex tone into a single channel, only those whichare 9 approximately octavely related. Table l shows an example of therouting of the individual partials of a highly 10 complex musical tonehaving a fundamental frequency 11 of 32.7 c.p.s. (C1) and 30 harmonicpartials. In the first 12 column is the harmonic number. The secondcolumn is the frequency in c.p.s. The fourth column identities 13 65 thenote nearest to the harmonic in the musical scale. 14 (Plus and minussigns show the direction of deviation 15 when coincidence is poor, andwhen the partial lies nearly halfway both note letters are shown.) Thethird column 16 22 19 27 shows which of the four octaphonic channelswill trans- 17 23 20 2g 70 mit the harmonic. Table 2 brings the variousharmonics 18 24 21 29 together into four octaphonic channels. The numberof harmonics in each channel varies from 5 to 10. In this 25 example theII channel, which transmits the fundamental 26 ao frequency, carriesfive of the first ten harmonics. Channels III and IV each carry two, andV has only one of the first ten. The next three harmonics go to channelIV. Although the lower harmonics are usually of greater amplitude thanthe higher harmonics, there are some complex tones in which the higherharmonics are significant. For this reason there is some advantage inlocating the output of channel IV adjacent to II. These two channelscarry ten of the rst 13 harmonics, and 13 of the first 18 harmonics.This is why channels III and IV are transposed in FIGURES 1 and 2, andfrequently throughout this application.

Another example will illustrate that it is also advantageous to havechannel II nearby when the fundamental frequency lies in channel IV.Table 3 shows a 20-harmonic tone of fundamental frequency 49 c.p.s.(C1), lying in channel IV. Table 4 groups the harmonics into octaphonicchannels. It is apparent that channel II has the same relationship to atone having its fundamental in channel IV as IV did to II in theprevious example. The small differences in the high harmonics arebecause G1 is in the middle of its quarter-octave filter range while C1is off center. The effects of harmonie distribution among the fourchannels upon tonal localization will be analyzed hereinafter inconnection with FIGURE 11.

FIGURE 4 is a simplification of FIGURE 3, which takes advantage of thenormal energy distribution in musical sounds, and of the relativeinaudibility of the very low-frequency difference tones generated bycombinations of signals in the lowest octaves of the musical scale.Tonal partials lying above C8 (approximately 4000 c.p.s.) are generallyquite weak, and can be omitted from the octaphonic filter system withoutmuch degradation in performance. The lower harmonics of the lower notesare sparsely distributed along the frequency scale in most music.Furthermore they are not easily localized by listeners and theirdifference tones are hardly audible. Therefore they can be combined asshown in FIGURE 4, with small degradation in purity of reproduction.Highpass filter 83 and low-pass filter 84 can be connected to amplifiersand loudspeakers designed specifically for their frequency ranges or,for the sake of economy, can be combined and mixed into all four of theoctaphonic channels. Preferably the loudspeakers in this case would beWoofer-Tweeter combinations with dividing networks, in order to avoidintermodulation distortion between widely separated frequencies.

An alternative means for separating the tonal components into-octaphonic channels is the use of multi-resonant filters. An example isa bank of suitably damped flexible, vibrating strings tuned to thetwelve equally tempered frequencies in a low octave of the scale. InFIGURE such a set of string filters 84-95 is shown schematically, withseparate input transducers 96-107 and output transducers 108-119. Theelectro-mechanical transducer usage could be simplified. A single inputtransducer T of high mechanical impedance could drive all twelvestrings, and each group of three strings could have a common outputtransducer, leading to channel amplifiers 75-78 and the correspondingloudspeakers 79-82. This system has the advantage that any givenamplification channel Iwill transmit all of the harmonics of a tonelying in its group designation. However some of the higher harmonicswill also be reproduced in other channels as well, so it will benecessary to attenuate the high-frequency response of all channels tocompensate for the multiple reproduction of the higher frequencies. Thechief advantage of this system is that only twelve filters are required,and they are of a type which can be sharply tuned at each resonancefrequency at relatively low cost.

The simplest application of the octaphonic principle to musicalinstruments is to instruments which generate each individual musical-wave form separately. The pipe organ is an example. If a small pipeorgan were to be amplified so as to fill a large arena, it would be aadvantageous from an intermodulation distortion standpoint to have allof the C, Cif, D pipes so arranged as to be picked up by one microphone;all of the Dfi, E, and F pipes by another microphone; and so forth. Eachmicrophone would be connected to its own amplifier and loudspeakersystem.

The counterpart for the various electrical and electronicWaveform-generating types of instruments is shown in FIGURE 6.Generators in bank 120, keyed on from the organ clavier, may be any typeof complete waveform generator, such as an electronic generator of acomplex tone spectrum, an electrostatic scanner of a variablecapacitance generator, a magnetic scanner of a specially distributed orrecorded magnetic waveform, a photoelectric pickup of a photographicimage of a musical waveform, and the like. In all of these the outputsfrom all of the Cs, Cits, and Ds in each octave of each stop would becombined (with reasonable care in isolation and loading) and amplifiedin amplifiers A and radiated separately from the other three groups oftones, in radiators R. Note in FIGURE 6 that the loudspeakers haveacoustically separate back spaces because they are mounted closetogether. Preferably the loudspeakers would be spaced apart as well aspartially enclosed so that intermodulation distortion resulting fromacoustical coupling between loudspeakers will be minimized.

Although the explanation of this form of octaphonic system for organs issimple and straightforward, this form of the system has the disadvantagethat each individual tone has less spatial spread than in some of thelater systems (e.g. FIGURE 9). Patent No. 2,596,258 separates the tonesof the scale into two groups for separate amplification and radiation,with alternate notes in the equally tempered scale going to differentchannels. The purpose of that invention was to prevent electricalbeating effects between tones having equally tempered intervals of aperfect 4th or a perfect 5th (e.g. C-F and C-G). The present inventiondiffers from Patent No. 2,596,258 in that the tones have a greatervariety of source locations. Furthermore the musical possibilities forintermodulation distortion are negligible in comparison to Patent No.2,596,258, in which a number of frequently used combinations of tones(eg. major third, augmented fifth) are amplified and radiated togetherwith attendant intermodulation distortion.

A simplification of the system of FIGURE 6 is shown in FIGURE 7. Hereall the lower tones in the scale are combined and supplied to amplifier121 and loudspeaker 122, specifically designed for low tones. In thisrange of playing the simultaneous tones are usually (although notalways) octavely related anyway, in contrast to the upper octaves wherechords are common.

In the system of FIGURE 7, the octaphonic division of tones is followedfor all tones above the lower tones, the division point being relativelyarbitrary. The amplifiers and radiators are accordingly denoted A and R,as in FIGURE 6.

In the formant type 0f electronic musical instrument complex waveformsare selected from a musical scale of generators (either keyed-on orkeyed-output, the latter being indicated in FIGURE 8) and are suppliedin combination to common stop (or tone-color) circuits prior toamplification. In other words the same electrical waveshaping net-Workis used regardless of fundamental frequency. This method of producingtone colors offers wide variety of timbre at relatively low cost,because the tone color filters do not have to be reproduced for eachnote or each octave. For the advantages of the octaphonic principle tobe realized in the formant type of instrument it is necessary only towire each octave of tone outputs in four groups, and to combine themoctavely in mixing circuits as shown in FIGURE 7. Each octaphonicchannel of signals is passed through an individual stop filter beforeseparate amplification. Connections from coupled Scales of generators orkey switches are made in the usual manner. Each stop (Y, for example)would employ four similar (but not necessarily identical) tone colorfilters Y2, YB, YQ, Y5 each receiving a different quarter of every 9octave. Stops X, W, U, and Y would also have 4 filters each. Stopswitches, whether on the input or the output f the filters, would be ofthe 4-pole type. Thus the octaphonic principle can be applied to theformant instrument simply by quadrupling the least expensive part of theelectronic system, the tone color filters.

Resonator organs of the type described in application for U.S. PatentSer. No. 46,704, filed in the name of Wayne, are ideally suited to theoctaphonic principle, because the organ already contains (for otherpurposes) an ideal set of filters for octaphonic use. Two notes of suchan organ are shown in FIGURE 9. Organ generator C1 supplies all thenecessary harmonics of a complex wave to common input point 124.Generator G1 does the same for common input 125. From these two commoninput points are connected many resistors 12Go, b, c, etc., and 127a, b,c, etc. which determine the amount of signal current supplied to theappropriate singly resonant circuits (or resonators) in circuit bank128. The circuits selected from this bank or resonant at or nearharmonic frequencies of the input tone waves. Thus the resistors 126a,b, c, etc. are spectrum shaping resistors for the note C1. Differentstops have different spectrum shaping resistor values for the samefundamental frequency. Only are stop is shown here for simplicity.However, no matter how many input circuits are connected to theresonator bank 128, the outputs of the individual resonators areconnected octaphonically in groups II-V, and amplified and radiatedseparately for minimum intermodulation distortion.

Referring now to the second object of the invention, assume that eachloudspeaker R in FIGURE 9 has been designed to have the best possibledirectional characteristic throughout its frequency range. Themultiplicity of channels, and the fact that no note is played on morethan one loudspeaker, allow the angular distribution of energy from thesystem to be just as uniform as one loudspeaker can provide. Eachloudspeaker is radiating a different set of frequencies, and can bedriven beyond the usual limitations due to non-linearity before audiblyspurious frequencies are generated. The necessity to combine loudspeakeroutputs in beaming arrays is obviated. When higher powers are required,the number of octaphonic channels can be increased to six or even twelvebefore any one channel duplicates the frequency of another.

FIGURE 10 is a simplification of FIGURE 9, in which all of the lowerpartials, irrespective of location within the octave, are combined forseparate amplification by amplifier 121 and radiation by speciallow-frequency loudspeaker 122. This simplification reduces the number ofvery low-frequency loudspeaker units required. Such units are usuallylarge and require large enclosurw, so reduction of their numberminimizes space requirements and cost. This simplification is possiblebecause chords are seldom played in the pedal section of the organ(except by virtuosos), and the difference tones generated by suchlow-frequency partials are too low in frequency to be audible.

The harmonic-synthesis type of electronic organ in FIGURE l1 uses a bank123 of continuous sine-wave generators which are tuned to the equallytempered scale. The generator outputs are wired to ganged key-switcheswhich provide simultaneous switching of a number of approximatelyharmonically related frequencies, eight in the case of FIGURE 1l.Because of the complexity in wiring of such a system, only three gangedkey-switches are shown for the simple case of a major triad, C2, E2, G2.The principal commercial type of harmonic synthesis organ employsharmonic drawbars. All of the first harmonics are normally collected andsupplied to drawbar No. 1, all of the second harmonics to drawbar No. 2,and so forth. FIGURE 11 shows how the octaphonic principle can beapplied to a harmonic synthesis organ, by using four sets of drawbarswhich (for convenience to the player) would be ganted, so that a singlemotion would be required for setting the relative amplitude of eachliarmonic, just as in present harmonic synthesis organs. Note that forC2 the output of the first harmonic switch goes to the first drawbar ofthe lowest set, and the output of the second harmonic switch goes to thesecond harmonic drawbar of the same set. However the output of the thirdharmonic switch goes to the third drawbar of the next higher set. The4th harmonic, being octavely related, goes to the lowest set ofdrawbars, but the 5th harmonic goes to the 5th drawbar in the third set.The seventh harmonic of C2 (frequently omitted in synthesis organsbecause the nearest equally tempered tone is grossly inharmonic) wouldbe routed to the 7th drawbar of the top set. Similar connections areshown for E2 and G2. This enables the partials of a harmonic synthesisorgan to be amplified and radiated octaphonically with audibleintermodulation distortion practically eliminated.

In the electronic organ field there is an entire class of modulatingdevices and circuits which make the electronically produced tone moreinteresting, more realistic, or more desirable aesthetically to thelistener. Examples are phase vibrato circuits, chorus or celestecircuits, reverberation circuits or systems, and random or non-periodicmodulators. It has frequently been found desirable to modulatedifferently in different octaves, as in Wayne Patent No. 3,004,460, andto radiate the different modulations separately from each other and fromthe original unmodulated signal, asin Wayne application Ser. No. 45,609.The octaphonic principle of frequency-range division provides advantagesover previous systems employing modulations in that the different (oruncorrelated but similar) modulation effects are applied to differentfrequencies within the same octave. FIGURE 12 is an example in which, inaddition, each individual complex tone will have space modulation withinitself. This is because some of the harmonics are being modulateddifferently from the basic group of harmonics which are approximatelyoctavely related. In FIGURE 12 the bank of singly resonant circuits 128of previous FIGURES 9 and l0 is the source of signals to be combinedoctaphonically. The scale of generators 120 in FIGURE 6, or the scale ofkey switches 123 of FIGURE 8, could just as easily have been used. Hadthey been, however, only the first advantage, i.e. different oruncorrelated modulation of different notes Within the same octave, wouldhave been achieved. In the case of the resonator organ the secondadvantage of modulation enhancement within the partial structure of asingle tone is also achieved.

Assume for discussion that the channel modulators in FIGURE 12 are phaseshift circuits 129-132, and that the channel modulators are under thecontrol of suitably filtered sources 13S-136 of random noise. Thesecould, of course, be dlifferent bands of noise from a single noisesource for simplicity and economy. The important thing is for themodulations to be independent or uncorrelated. If a triad C, E, G, ofpure flute tones is played, in which only the first harmonic partial isof audible amplitude, the corresponding tones will be radiated byloudspeakers 79, 81, and respectively. The phase modulations of eachtone will be independent in magnitude and time. At any instant any pairof tones may have phase shifts which are even opposite in direction.When these phase shifts are reflected into the acoustical standing wavesystem of the listening room, it will sound to the listener as if thethree tones in the triad are quite independent of each other. When morecomplex tones (such as diapason, string, -or reed types) emerge from theresonator bank 128, a majority of the energy of any given tone willgenerally go to one channel. Howe-ver smaller parts of the energy of thesame tone will be routed to other channels (refer to Table 4), and willtherefore be modulated somewhat differently. Thus for complex tones theindependent modulation of sub-groups of partials, combined With theradiation of these partials from spaced loudspeakers, gives eachindividual complex tone an apparent location l1 which is variable intime and space about the normal location which would be observed if themodulations were turned off. This adds greatly to the liveness of themusical tone heard by the listener. Moderate amounts of modulation makethe tone resemble pipe organ tone. Greater modulation gives a novel,musically interesting elfect.

When the complete audio-frequency spectrum, such as the output of asingle division of an electronic organ, is radiated octaphonically, theapparent location of the individual tones will depend upon (a) thenumber of octaphonic channels (four, six, or twelve), (b) the type ofelectronic organ (waveform generator, formant, resonator, harmonicsynthesis), and (if the organ is a resonator type) (c) the degree ofcomplexity of the tone spectrum radiated. The listeners ability tolocalize sounds coming from each of the channel loudspeakers will dependupon the angular spread of the loudspeakers, as seen by the listener,and upon the acoustics of the listening space.

For the waveform generating yand formant types of organ all of theharmonics of a given fundamental frequency will be radiated by the sameloudspeaker system. Consequently the listener will localize the tonalsources more definitely than he would when listening to the octaphonicoutput of a resonator organ, for which the motion effects of the oneorgan division are shown in FIGURE 13. Each square in the diagramrepresents the location of a channel loudspeaker identified by thechannel number underneath. No Ivertical motion is in- Itended to beimplied by the four horizontal bands lwithin each square. This is simplya convenience for showing what the situation is with regard to each ofthe four note-groups in a four-channel octaphonic system. Table 4 haspreviously shown how the harmonics are distributed among the four outputchannels for a complex tone having twenty harmonics. If only thefundamental has an audibly appreciable amplitude, the listeningsituation is the same as for waveform generating or formant types oforgans. .Each tone will come from the particular loudspeaker associatedwith its note-group. At the other extreme are tones having manyprominent harmonics. Seldom is the spectrum so highly developed as asawtooth tone valve, in which the spectrum level has a negative slope ofsix db per octave. More stringent tones than the saw-tooth Wave tend tobe musically unpleasant, and the unfiltered saw-tooth itself bordersupon this condition. In FIGURE 13 the saw-tooth wave has been assumed asa kind of upper limit on the distribution of energy into the higherharmonics for calculating a center of gravity for the power distributedywithin a highly complex tone wave, taking into account the harmonicdistribution shown in Table 4. For notes in Groups III and IV 84% of thepower radiates from the loudspeaker of the same designation. Ten percentof the power radiates from the adjacent end loudspeaker, and fourpercent from the other end loudspeaker, with a mere two percent from thefourth loudspeaker. Although the spectral energy is somewhat spread, thecenter of gravity is squarely in the center of the appropriateloudspeaker. The situation is slightly diiferent for channels II and V.Here there are no loudspeakers on one side to provide a balancingcontribution. Consequently the centers of gravity for a highly complextone lie slightly inside the actual loudspeaker locations. For lesscomplex tones, in general, the center of gravity will lie between thecenter of the end loudspeakers and the dots shown for the saw- Thecalculations on energy center of gravity are not intended to imply thata listener will localize the sounds strictly on a basis of energycentroid. The ability of listeners to localize sound distributed inspace, and especially the mechanisms by which this is accomplished, arestill not fully understood. However, the difference between anoctaphonic tone radiation system and a fourparallel-channel toneradiation system (in which all of the tones are radiated equally fromall of the loudspeakers) can easily be heard and demonstrated. In theoctaphonic system musical denition is greatly enhanced, and the soundsare more interesting, even to the musically naive observer. Thisadvantage is in addition to the freedom from intermodulation distortion,.and the freedom from the undesirable effects of arrays of multipleloudspeakers radiating the same sounds.

FIGURE 14 is an example of the use of the octaphonic principle in amulti-manual electronic organ. It shows an advantageous distribution ofthe loudspeakers in a three-manual organ consisting of Great, Swell, andChoir divisions. The Pedal division has been omitted from thediscussion, but it could be combined with the Great division, or itcould have its own widely distributed loudspeakers. The purpose here isto make the Great division sound large in comparison to the Choirdivision, with the Swell division intermediate in apparent size. Thedashed lines enclose the Choir division and the Swe-ll division. Thehorizontal spread is much greater in the Swell division than in theChoir division. A vertical spread has also been provided for the Greatdivision by duplicating its loudspeakers at a lower altitude. However aneven better arrangement than the one shown in FIGURE 14 would have theGreat division divided into six or twelve octaphonic channels, andspread over the same area shown in FIGURE 14. This would conserve theadvantage in directional characteristics while enlarging the Greatdivsions apparent size. Note that the group numbers have the reversenumerical order, left to right, in the Great division. This balances onedivision against the others when the full organ is played, utilizing thefull solid angle available, no matter what chords or progressions aremost probable in the key of the musical selection being played.

Many other refinements and extensions of the invention within the scopethereof, will occur to those skilled in the art. It is intendedtherefore that the scope of the present invention not be limited by thevforegoing disclosure, but rather by the appended claims.

Iclaim:

1. In a loudspeaker arrangement for an organ system having a greatdivision and at least one small organ division, comprising an extendedarray of octaphonically arranged speakers for said small organ division,an array of octaphonically arranged speakers for said great divisioncomprising four speakers arranged -two on one side and two on anotherside of said first mentioned array.

2. The combination according to claim 1 wherein the rst mentioned arrayhas a predetermined octaphonic group number order and said secondmentioned array has the reverse octaphonic group number order.

3. In a music system, a source of music signals comprising a source ofplural complex tones, a plurality of string iilters connected inparallel with each other and in cascade with said source of pluralcomplex tone, and means for acoustcally radiating the outputs of saidstring filters, wherein is provided means for octaphonically combiningthe outputs of said string filters in separate channels, and means foracoustically radiating the outputs of said channels via separateloudspeakers.

4. In a musical system, a transducer of music signals extending over awide multiple octave audio spectrum, p

a plurality of quarter octave filters connected in cascade with saidsource and in parallel with each other,

means for combining in separate channels, outputs of said lters havingprimarily octavely related partials, and

means for separately transducing the signal content of said separatechannels.

5. The combination according to claim 4, wherein said means forseparately transducing are loudspeakers.

6. The combination according to claim 4, wherein said 'means fortransducing are magnetic tape recording means.

7. The combination according to claim 4, wherein said transducerincludes plural magnetic tape recorders, one for each of said quarteroctave lters.

8. In a music system,

a transducer of music signals extending over a Wide multiple octaveaudio spectrum,

means for separating from said music signals into separate channelsspectra having primarily octavely related partials which are alsoimmediately adjacent in frequency and which extend over no more than onethird of an octave, and

means for separately transducing the signal content of said separatechannels, respectively.

9. In a magnetic tape recording and reproducing system,

a source of a Wide band of frequencies representing audio, lter meansfor dividing said wide band of signals into sub-bands, each of saidsub-bands including a quarter octave of frequencies and said sub-bandsbeing substantially non-overlapping and immediately adjacent,

means for combining in separate channels the outputs of those of saidfilter means which have primarily octavely related partials, means forseparately magnetically recording the outputs of said channels asseparate tracks of a tape,

means for separately reproducing the signal content of said tracksincluding a separate reproducer head for reading out each of saidtracks, and

a separate loudspeaker coupled to each of said reproducer heads.

10. The combination according to claim 9, wherein said loudspeakers arearranged in a spatial array such that only two of said loudspeakershandling immediately adjacent frequencies are immediately adjacent eachother.

11. In a magnetic tape reproduction system, for reproducing from amagnetic tape having a track containing a recorded multi-octave audiosignal,

means for reproducing the content of said track into a single channel asa broad band electrical signal,

iilter means for dividing said broad band electrical j References CitedUNITED STATES PATENTS 2,596,258 5/1952 Leslie 84-1.01 2,982,819 5/1961Meinema et al. 333-71 X 3,327,043 6/1967 Martin 84-1.01 1,550,684 8/1925Espenschied. 1,961,410 6/1934 Wegel 333-71 X 2,803,800 8/1957 Vilbig333-71 X HERMAN K. SAALBACH, Primary Examiner S. CHATMAN, JR., AssistantExaminer U.S. Cl. X.R.

4 slt- 1.03, 1,14

